1. Field of the Invention
The present invention relates to a device for controlling micro fluid, in particular, relates to the device for exchanging minimum amount of the fluid only by using surface tension of the fluid instead of external force like a pump.
2. Description of the Prior Art
The microfluidic control implies doing various handlings, such as the feeding, stopping, exchanging, or mixing of the microfluids in very small channels or chambers. The microfluidic devices, in which such microfluidic controls are accomplished in a single chip, are called LOC(Lap-On-a-Chip), and they perform specific functions like biochemical reaction, mixing, or detection, etc., by controlling the micro fluid. Examples of the microfluidic device include various bio chips such as a protein chip, a DNA chip, a drug delivery system, and a micro biological/chemical reactor.
The microfluidic control is achieved by various operating principles. For example, the microactuating method by which a micro pump and valve are mounted on a channel or chamber, the electrophoretic/electroosmatic method by which a voltage is applied along a fine channel to move the fluid, or the capillary flow method using capillary force are possible. The devices for controlling the micro fluid are classified into the active and passive microfluidic components. The active fluid control is achieved by the active microfluidic components such as a micro pump or valve driven by electricity and external mechanical forces. However, the passive microfluidic components use natural forces and the fluid control in those components is achieved by surface modifications or geometrical variation of channels or chambers.
The device which uses the capillary force as a driving force is a passive element. It stops and feeds the fluid, and even adjusts the flow speed, according to the principle that attractive and repulsive forces are naturally produced by the surface tension between the fluid and inner surfaces of the fine connecting channel. It is because of the property of the surface tension that the surface tension is used for a micro fluid control. In other words, as a ratio of the surface area to a volume becomes high in a very small sized fluid system, a force associated with the surface, especially the surface tension produced when a free surface is formed on the fluid, can play a relatively much greater role than that of other forces. Also, the fluid control using surface tension has several advantages. For example, there exists no driving elements, thereby additional power supply is not needed, and when it is applied to a biochip, not only a instrument thereof can be small sized but manufacturing and operating costs of the instrument can be reduced and the instrument is hardly out of order.
Because of the characteristics and advantages of the fluid control using the surface tension as described above, the principle of the surface tension is applied to many micro fluid control systems. For example, the systems include a micro stop valve, a micro pressure sensor, an micro-accelerometer, a micropump, fluid feeding, fluid filling, an inkjet, a robot probe, a MOEMS equipment, an optical shutter, a micro switch, etc.
However, the fluid control only using the surface tension has disadvantages. For example, the fluid control is sensitive to geometry and surface condition, and since it has no external force, it is difficult to exactly control time and flow control. Especially, as the surface tension occurs on the interface between liquid and gas, additional force can not be applied to the liquid portion already filled, thereby the control has some limitations. Therefore, most devices using the conventional surface tension utilize the surface tension only as a driving force for feeding the fluid or as a means for stopping the fluid. Further, a device has been complemented by coupling with an active type device such as a pump.
Typical examples of a device for controlling fluid using capillary flow are as follows. See the following publications which are incorporated herein by reference: U.S. Pat. No. 6,143,248 entitled “capillary micro valve” issued Nov. 7, 2000; U.S. Pat. No. 6,271,040 B1 entitled “diagnostic devices method and apparatus for the controlled movement of reagents without membranes” issued Aug. 7, 2001; U.S. Pat. No. 6,296,0020 B1 entitled “fluid circuit components based upon passive fluid dynamics” issued Oct. 2, 2001; and U.S. Pat. No. 6,113,855 entitled “devices comprising multiple capillarity inducing surfaces” issued Sep. 5, 2000.
The U.S. Pat. No. 6,143,248 entitled “capillary micro valve” has disclosed the micro valve for feeding micro fluid from a micro storage chamber to a transferring channel by means of the adjustment of channel size and centrifugal force based on the principle of capillary and centrifugal force. The U.S. Pat. No. 6,271,040 B1 entitled “diagnostic devices method and apparatus for the controlled movement of reagents without membranes” has disclosed a diagnostic biochip structure, in which the samples are feeded only using the capillarirty and react in chambers and connecting channels, fordetermining the existence of sample reaction in optical means. The U.S. Pat. No. 6,296,0020 B1 entitled “fluid circuit components based upon passive fluid dynamics” has disclosed a structure capable of stopping the fluid using the hydrophobic material or the abrupt expansion of connecting channel within the capillary tube. The U.S. Pat. No. 6,113,855 entitled “devices comprising multiple capillarity inducing surfaces” has disclosed a technical idea that produces capillary force by suitably arranging hexagonal micro columns in chambers.
However, the above referenced patents use the surface tension only as a simple passive means for driving the fluid or a means for stopping the fluid by controlling the capillary force based on a geometrical change of the connecting channel or a surface modification.